I was researching a fun post about the apocalypse today when I suddenly came across a disaster scale I’d never even heard of before. It’s the Volcanic Explosivity Index, which is a way of measuring the magnitude of volcanic eruptions via the amount of ejecta they produce – not a perfect way of ranking volcanic eruptions, if you ask me, but probably the only one that’s really possible given all the different ways a volcano can explode. It then struck me that it might be a good idea to spend a little while talking about the major disaster scales and why they’re set up the way they are, since it’ll be a good setup for whenever I do get around to the apocalypse, as well as ensuring that next time you read a news report about an earthquake you’ll have some idea of what the experts mean when they say it measured 5.8 on the Richter scale.

So let’s start with the Richter scale, which is the obvious one everyone thinks they know about. The Richter scale operates on a logarithmic scale, which is a method of measuring quantities that increase exponentially while keeping them all on the same piece of graph paper – or in this case, on the same ten point measurement device. This means that each point on the Richter scale represents an increase of ten times the power of the previous point on the scale; an earthquake measuring 3.0 on the Richter scale is ten times more powerful than one which measures 2.0, and a hundred times more powerful than one which comes in at 1.0. It’s this measurement quirk more than anything else that leads to most local reported earthquakes coming in at around the 4.0—5.5 mark, since the scale has to cover the entire range of possible earthquakes from tiny microtremors to vast world-ending ruptures in the earth’s crust. 4.0 is the point at which earthquakes become noticeable by the majority of humans, and at 5.0 they start causing minor property damage; these sound like large numbers on a ten point scale but you have to remember that even a 5.0 earthquake is a thousand times less powerful than the 8.0s which cause tsunamis and kill thousands of people in places which are – hopefully – a long way away.

Anyway, what you should take away from this is that the first six points on the Richter scale represent comparatively weak earthquakes that have little chance of killing anyone; the news reports are usually just quoting them to make them seem bigger than they really are. The lethal stuff doesn’t really start until after 6.0, and the good news is that you only tend to experience one of those if you live in close proximity to a tectonic plate boundary. I would also draw your attention to the final point on the conventional Richter scale – 10.0 – which says that an earthquake of this magnitude has never been recorded. That’s not to say it can’t happen, just that it would take something rather extraordinary to prompt that sort of geological upheaval, like the earth being walloped by a bloody great asteroid. We don’t notice earthquakes below 4.0 and the range of known earthquakes only goes up to 9.9, so as far as most people are concerned the Richter scale actually operates between 4.0 and 9.9, and suddenly your local earthquake measuring 5.1 on the scale doesn’t really seem like all that much.

Then there’s the Volcanic Explosivity Index, which works much the same way as the Richter scale (except at lower bounds between 0 and 3 due to the way low-end volcanic eruptions work) except it measures the quantity of volcanic ejecta rather than the amplitude of the shockwaves passing through the earth. The difficult thing to get your head around here is that the VEI measures things in terms of volume, and it can be quite hard for the human mind to comprehend just how large a cubic kilometre of ash really is. It’s one of the questions of scale that often trips up undergraduate physicists, actually¹: how many cubic metres go into a cubic kilometre? The answer isn’t a thousand, as a lot of people think; it’s actually one billion, which is a very large number of cubic metres indeed.

Now, unlike earthquakes volcanoes are usually only locally devastating in the short-term, which is one of the reasons why the VEI is focusing on the amount of ejecta – or in other words, the amount of ash – they release. Not only is this a handy way to rank the violence of a given volcano’s eruption, but it’s the ash and gas output over the long-term that will do the major damage on a global scale.  Eyjafjallajokull shut down all flights over Europe with its ash when it erupted in 2010, and that ranks at a relatively titchy 4 on the Volcanic Explosivity Index with 0.1 cubic kilometres of ash output. Krakatoa in 1883 turned the skies around the world an attractive shade of blood red and dropped global temperatures by a full degree Celsius – and Krakatoa only comes in on the VEI index at six out of eight. Once you get out to eight out of eight – the so-called supervolcano eruptions of Yellowstone and Toba, each spewing out over a thousand cubic kilometres of material – you start to see why volcanic eruptions can be globally threatening events. Both Yellowstone and Toba spread so much ash into the atmosphere and onto the Earth’s surface that not only was there a significant drop in the global temperature for years afterwards, but the human, animal and plant populations of the world started to suffer mass dieoffs as the ash either polluted their food/water sources or made it impossible to get enough light to grow. There’s even a theory that posits Toba was responsible for reducing the human race to just a few hundred living individuals, which is why the seven-billion-odd modern humans are descended from a relatively small number of ancestors. Personally I think this is just a little bit too sensational, but it’s inarguable that supervolcano eruptions on this scale would seriously mess up civilization as we know it.

Finally there’s the Torino scale, which is used to rate asteroid impacts. Given that the vast majority of asteroids tend to miss the Earth completely, the Torino scale differs from the others in that it combines both the potential magnitude of the impact event with the probability that the asteroid will actually hit the Earth to produce a single number that indicates just how much we should be worrying about it. Small asteroids that will definitely hit us but will burn up in the atmosphere rank in low positions on the Torino scale. Large asteroids that could explode a small country but which have low probabilities of impacting are also ranked in low positions on the Torino scale. It’s only a combination of a (reasonably) large asteroid and high probability of impact which results in an asteroid having a Torino number attached to it which is larger than one, and if you look at the chart it is impact probability which is the dominant factor in an asteroid managing to place on the higher regions of the scale.  Which is fair enough, really; an object with a 1% chance of impact is something we should definitely keep our eye on, but until we get improved observations of its trajectory and know for sure it’s not a huge worry unless it’s something large enough to potentially end all life on Earth.

So any object with a Torino scale value of 1 or 0 is basically completely non-threatening, and as far as I’m aware the only asteroid that has made it past 2 was 99942 Apophis back in 2004, which was briefly ranked at 4 due to its size (350 metres diameter, which isn’t world-ending but is still pretty big) and the fact that it had a whopping 1% chance of impacting. That it was eventually downgraded to zero should tell you something about the Torino scale: since the bottom four rungs of the scale are based on impact probabilities calculated before detailed observations, this range of numbers basically exists to tell astronomers what they should be focusing their attention on and not to panic the general public. Not that this stops the media from completely misinterpreting what the scale means, of course;  they actually had to rejig the scale categories at one point because asteroids with a Torino value of 1 kept cropping up in news reports as potential threats when in fact these objects posed no unusual danger and just needed a double-check to make sure there was no chance of them hitting.  (This is why 1 is now in its own category as “NORMAL” instead of “MERITING FURTHER ATTENTIONS OF ASTRONOMERS”.)

But what about the upper regions of the scale? It’s the last three points we should really be interested in, which represent certain impacts with increasing levels of destructiveness. Number 8 is localised destructive potential, which basically equates to the detonation of a large nuclear weapon – annoying if you happen to be standing nearby, but not unduly threatening to everyone else. Number 9 represents regional  destructive potential, which is… hmm. If it was an ocean impact we’d probably be talking about something on the level of the 2004 or 2011 tsunamis, but I’m not sure there’s a good analogue for a land impact. Earthquakes don’t really translate that well into asteroid strikes, but maybe just imagine a similar level of devastation to one which wrecks an entire country (so Haiti 2010, Lisbon 1758 etc.) and you’d have some idea of the amount of damage we’re talking about. And then there’s a Torino number of 10, which has the interesting wording of global climactic catastrophe.   An asteroid that ranks at 10 doesn’t have to be large enough to kill millions of people through direct impact damage (although it probably would just as a byproduct), it just has to be able to throw up enough impact debris to cause mass species dieoffs similar to a supervolcano (or a nuclear winter).

Now, if you ask me there should be a number beyond 10. An impact of 10 on the Torino scale is small enough that it still leaves a fair chance of survival for the human race, albeit with vastly reduced numbers. If there was an impact event powerful enough to crack the earth’s crust open there’d be no survivors whatsoever, so maybe there should be a number 11 in its own category of “WE’RE SO SCREWED”. On the other hand the Torino scale exists to communicate information to the public and I suspect the public would find the existence of this category profoundly depressing, so perhaps it’s for the best.

——————————————————

The post How To Measure The End Of The World. appeared first on The Scientific Gamer.

After spending not a few words talking about Armageddon and fake space rocks last Wednesday I was slightly surprised when an actual real-life asteroid tore through the skies above Russia and disintegrated/detonated in midair somewhere above Chelyabinsk. Thanks to the asteroid’s passage over populated areas and the modern ubiquity of smartphones with some kind of video capture capability – not to mention the uniquely Russian preponderance of car dashboard cameras to provide some protection against the now-famous driving standards in the country, as well as the notoriously corrupt traffic police – this has been by far the most well-documented asteroid “strike” in history, so I thought I’d take a little while to talk about it, and the reaction to it.

First, there’s the question of nomenclature. I’m going to be calling the Russian object an asteroid in this piece, but you should know that the term “asteroid” is rather ill-defined (in fact all the terminology used to refer to things smaller than dwarf planets is rather ill-defined), and the best I can come up given currently-existing IAU guidelines is “a lump of rock that is smaller than a dwarf planet but larger than a meteoroid”. Meteoroids are currently defined as “a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom”, but that definition dates from 1968 and we’ve since determined that meteoroids and asteroids are basically the same population of bodies, with the term “meteoroid” being used to refer to any small-scale asteroid (10m or below) that manages to enter Earth’s atmosphere. Most meteoroids burn up in the atmosphere; the ones that make it through to hit the ground are called meteorites, which is what the majority of the press is calling the Russian asteroid.

Are they correct? Well, yes and no. There are two problems with calling the Russian asteroid a meteorite:

1)      It was actually quite large – NASA says around 17 metres – which puts it out of the generally accepted size range for a meteorite.

2)      It didn’t actually hit the ground. While it didn’t burn up completely, the Russian asteroid broke up just above ground level thanks to the immense heat and pressure of entering the atmosphere.This will have scattered chunks of asteroid everywhere and there’s already been several fragments and craters reported found. Astronomers have a specific term for asteroids that create fireballs and break up in the atmosphere like this: we call them bolides.

However, if the press went around referring to the “Russian bolide” in their news reports nobody would have any idea what the hell they were talking about, so in the absence of any better term calling it a meteorite is fine. This is the IAU’s fault for not ever bothering to classify small Solar System objects properly and relying on fuzzy definitions that are decades-old, not bad reporting.

Now, let’s take a moment to watch a video of the asteroid’s passage.

(I have desperately tried to avoid lifting the video links straight from Bad Astronomy guy’s excellent rundown of what was going on at the time, but the originals I saw have since been buried by recycled clips from news agencies and I didn’t save them for future reference.)

That gets across just how bright the asteroid’s entry into the atmosphere was; it’s a large object travelling at around 18 kilometres per second (i.e. far, far faster than a supersonic jet aircraft, which would be lucky to manage a kilometre and a half per second) so it’s generating an awful lot of ram pressure, which heats up both the asteroid and the air flowing around it. If you direct that amount of force and energy against a lump of rock and metal it is rather understandably going to start falling to pieces, which is exactly what the Russian asteroid did; it lasted barely thirty seconds in the Earth’s atmosphere and broke into bits over the Urals near Chelyabinsk. But did it explode?

This video shows that there was a very large bang about thirty seconds after the asteroid’s passage through the atmosphere. This is caused by a sonic shockwave, which is what broke all the windows, smashed up that zinc factory and injured a thousand people, but the shockwave is not the product of the asteroid exploding or hitting the ground. Instead it’s been caused by the simple passage of the asteroid through the air at such a ridiculous speed. You’ve heard aircraft make sonic booms as they break the sound barrier? This is that, except magnified about a hundred times. The shockwave of a sonic boom is created by air piling up in front of the aircraft, and as the aircraft goes faster and faster the air simply cannot get out of the way fast enough and becomes compressed into a single shock front moving at the speed of sound. Since the aircraft is moving faster than the speed of sound you’ll see a supersonic jet a few seconds before you hear its sonic boom. Scale up from an aircraft to a large chunk of rock 17 metres on a side, and make the time lag thirty seconds (because it was around 30-50 kilometres up, an altitude much higher than aircraft fly at) and you get the shockwave caused by the Russian asteroid.

So the bang wasn’t caused by any explosion in the conventional sense; it’s not like the asteroid reached the end of its trajectory and abruptly exploded like a nuclear weapon. Instead, as bits and pieces sheared off of the asteroid it would have released energy with the same effect as a trail of smaller explosions. NASA puts the total energy released during the asteroid’s passage through the atmosphere at around 500 kilotons, which is roughly equivalent to a mid-sized nuclear bomb, but this energy was released gradually instead of all in one go which is why the property damage was mostly limited to a lot of smashed glass.

That’s what we think happened, but sadly there’s a couple of myths that have already grown up around the Russian asteroid:

• That it was something to do with the asteroid 2012 DA14, which was scheduled to make a very close approach to the Earth on the same day. This is stupid because the two objects were on completely different trajectories as demonstrated by this video; the Chelyabinsk asteroid grazed the Earth’s atmosphere on an east-west trajectory, while DA14 passed it by north-south. They are completely different bodies that just happened to get noticed by the human race on the same day; thousands of meteoroids/meteorites enter the Earth’s atmosphere every year and the vast majority of them are completely unknown to us because they burn up too high, or they come in during the day, or they descend over the ocean. The only things that make the Russian one special are its size and that it happened to come down over a populated area.

• That it was intercepted by Russian air defence forces and destroyed. This is insane for a number of reasons but I’m going to pick the most salient one: the best air defence technology on earth currently cannot make a reliably successful interception on an ICBM moving 7-8 kilometres per second. It would have no chance of hitting an asteroid moving at 18 kilometres per second.

Finally there’s the media reaction to it, which if you look past the usual idiotic misreporting is basically one of total ignorance. Despite reporting on 2012 DA14 for a week or two the fact that an asteroid could actually make it through (most of) the atmosphere and cause some damage to a populated area seemed to take them by surprise. I lost count of the number of hastily-commissioned opinion pieces I saw which basically said “Whoa, maybe we should be a bit worried about this!” like they previously thought it was something that only happened in movies. The good news is that even if 2012 DA14 had hit it would have caused only localised damage (roughly equivalent to one city, and that’s only if it had managed to score a direct hit), and that really threatening impacts only occur over geologic timescales. The bad news is that there is literally nothing we could do to stop either kind of impact without a decade of lead time to prepare – and as the Russian asteroid showed, often we don’t even see them coming at all.

(Just as an aside, every news article under the sun mentioned the Tunguska event as another meteorite event which happened in Russia, but nobody brought up the Sikhote-Alin meteorite which came down over what was then the Soviet Union in 1947. Unlike Tunguska this was witnessed by people who understood what they were looking at, including an artist who immediately drew this. It’s strikingly similar.)

The post Asteroids Again. appeared first on The Scientific Gamer.

gnomishlich asks

Armageddon, terrible movie about oil drillers on an asteroid how would a space shuttle or other space traveling vehicle fare for persons odds of arrival, survival, and departure from an asteroid?

Oh god, what have you done. WHAT HAVE YOU DONE.

You may think Armageddon is a terrible movie, and you would hardly be wrong to do so. Michael Bay’s job is to make blockbuster movies that make extensive use of special effects and loud action scenes to cover up the fact that they have no logical plot or consistent characterisation to speak of, and are designed to cater to people whose brains are operating on the mental level of a twelve year-old boy. Literally every single one of his films has been offensively bad. Like, not just the regular kind of bad, where you sit through it and it’s bad and at the end of it you think “Well, that was bad, I won’t be watching that again.” No, that would be too easy for Bay, and in fact if he ever made a film that was simply bad I’d think he was slipping somehow. What sets Bay’s films apart from the rest of the lowing, braying herd of CGI summer blockbusters is that they seem to be designed to piss the audience off. I honestly don’t know how you can watch a Transformers film and be anything other than utterly and completely ashamed and insulted – ashamed because you spent two-plus hours of your life watching this crap and you don’t want anyone else to know, and insulted because Michael Bay thinks you are stupid enough to enjoy something pitched at the level of a Transformers movie. It’s only a Michael Bay film that can make me feel soiled somehow after I’m done watching it, like I need a day-long shower to wash off all of the dumb that has built up on my skin. It’s hard to accurately recall just how horrible I felt after watching Transformers 3, but thanks to the internet my immediate reaction has been preserved for posterity:

Transformers 3 should be submitted to a peer-reviewed scientific journal because it conclusively proves many things that otherwise would have taken decades if not centuries of study and observation. The intellectual bankruptcy of Western civilization and culture. The non-existence of God. The ultimate futility of living in a world where the laws of physics allow such crimes to be perpetrated against the very nature of the universe. Like some sort of Lovecraftian horror that has slithered forth from an unholy nether dimension, Transformers 3 is so utterly and fundamentally at odds with everything good and sane that the mind atavistically recoils and refuses to comprehend it.  And even if I manage to purge the experience of having watched it from my memory it will still leave signs of its passage; a broad swath of tainted brain matter that cannot be reused for any other purpose but which instead grows and expands, subverting healthy tissue and corrupting my mind to its vile purpose until I am a twisted ur-man no longer capable of rational thought. Ia! Ia! Baythulu fhtagn!

Right. Yes. Anyway. Michael Bay films. Very bad. Very bad. Armageddon is a bad film, and it is no less bad for having been made during Bay’s early period (it was his third film or something), but by the standards of Michael Bay it is unremarkably bad. There’s nothing to make it stand out in terms of badness from the likes of Pearl Harbor or The Island – yes, it’s stupid, and shot with Bay’s trademark oversaturation of American flags fluttering in the breeze, and the scene with the minigun makes no logical or rational sense, but neither do any of his other films so there’s nothing here to mark it out as different in any way.

That is, unless you happen to have a PhD in solar system impact physics, at which point Armageddon becomes tied with Mission to Mars for the Worst Cinematic Atrocity Perpetrated Against Science award. You’ve got an unrealistically sized asteroid heading towards Earth which is stated to be “the size of Texas”, so about 700 miles across, except there’s only one asteroid (now dwarf planet) in the belt anywhere near that big and we’d notice if anything happened to it. The asteroid has been knocked out of its orbit by a comet; this is a chunk of ice which is typically Not Very Big and has sod all mass thanks to being made of spongey ice, and would have little impact on the orbital trajectory of a an asteroid 700 miles on a side¹. The asteroid itself looks nothing like an asteroid that’s just been walloped by a comet; there’s a few chunks of rock and clouds of debris orbiting with it like you’d expect, but I don’t think any asteroid would look quite as spiky as the one in Armageddon does. It should look just like a big rock, or like a big pile of agglomerated rubble compressed down into a sphere by its own self-gravity. Instead it looks all gothic and nightmarish and there’s lots of weird green and blue hues used in the lighting (again, trademarks of Bay) because that shit looks cooler, I guess.

Then you’ve got the actual asteroid impacts on Earth, which are also awful. The one at the start creates a moving wall of fire that eventually consumes the entire planet, and I don’t even know how this would work. Asteroid impacts tend not to be about fire so much as they are massive earthquakes and huge blast waves. Oh, anything caught nearby is going to be a crispy critter (read the first statement from a witness of the Tunguska event) thanks to the immense heat of the asteroid’s entry into the atmosphere and sheer quantity of energy liberated when it either hits the ground or explodes in an airburst, but we’re talking something about the size of a big nuclear fireball here, and not some all-encompassing global catastrophe. While the shock waves would devastate an area hundreds or thousands or miles around the impact site, truly global damage would be done through dust clouds/climate change for the smaller asteroids, and the physical disruption of the Earth’s crust for the larger ones.

The second thing this – and all other Hollywood films about asteroids, including Deep Impact – gets wrong is the speed of the asteroid. Asteroids in films move slowly, almost leisurely, like an out-of-control jet airliner rather than a piece of space rock moving at 20-30 kilometres per second. People on the ground have plenty of time to see them coming and make futile attempts to escape. In reality, unless the asteroid comes in at an incredibly oblique angle the time lag between an asteroid entering the Earth’s atmosphere and hitting the ground is about one second. Try snapping your fingers once; that’s how fast an asteroid impact would seem to a watching human. If they’re standing close enough to see it happen they’re screwed, and even people who are safely over the horizon will be killed by a blast wave pushing a wall of moving rock and debris towards them faster than the speed of sound. Even smaller asteroids (and we’re talking the metres-scale stuff that makes it to the ground here) would pack enough punch to explode with the force of a moderately-sized stack of TNT. You see the Barringer Crater? The thing in North America that’s over a kilometre wide and 200 metres deep? We think the rock that created it was about fifty metres in diameter. Fifty. Metres. Just one of the “tiny” rocks featured at the start of Armageddon would devastate a significant area of New York if it managed to score a direct hit, rather than just chopping the top off of the Chrysler building. Movies dramatically understate how lethal and destructive asteroid impacts are. It’s one of the many cases where the reality is actually far more terrifying than what’s on film, but it’s deliberately understated so as not to scare the living daylights out of the audience.

And then we get to your question, which is: could we fly a spacecraft up to an asteroid and land on it? The answer is, yes we can. In fact we have, and they even managed to get the spacecraft back to Earth orbit afterwards. Armageddon’s rendition of military space shuttles that handle like jet fighters in outer space is completely ludicrous, of course, but we’ve managed it with a robot probe so there’s absolutely no reason why we couldn’t do with an appropriately-designed manned spacecraft. Before the Orion program was gutted by the US administration one of the proposed missions was a trip out to a Near Earth Object – in other words an asteroid orbiting relatively close-by to the Earth (out past the orbit of the Moon, but not too far out) – so it’s something that is seriously considered by space agencies today, and it’d actually be considerably safer than a trip to Mars thanks to the shorter mission duration and the fact that “landing” on an asteroid doesn’t mean marooning yourself at the bottom of a gravity well.

This is what happens when somebody mentions Armageddon to me; I spend 1500 words ranting and then finally get around to actually answering their question in a single paragraph. The movie’s science was deconstructed years ago by somebody with far more patience than me², and it used to be shown to new management hires at NASA as a training exercise to see how many inaccuracies they could spot. It is quite literally the textbook case of How Not To Do It. Please, nobody ever bring it up on here again.

(Incidentally if you want to know if we could use Armageddon as a blueprint for saving the world from a real rogue asteroid, I already covered it in a previous post.)

————————————————————————-

The post Armageddon Ist Verboten. appeared first on The Scientific Gamer.